1. Field of the Invention
The present invention relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming capable of effectively reducing mechanical stresses to developers during a transportation for a development to reproduce a superior quality image.
2. Description of the Related Art
A development device using a dry developer containing at least a toner is known in the field of an image forming apparatus using an electrophotographic technique, such as a copying apparatus, a facsimile machine, or a printer. In a known development device, a toner agitated in the development unit is deposited on the surface of a developer carrying member such as a development roller or a development sleeve, is formed in a uniform thin layer by a thin layer forming member such as a thin layer forming blade, and is conveyed to a development zone facing a photoconductive body as a latent image carrying member to develop a toner image from the latent image on the photoconductive body. Subsequent to development, the toner not transferred to the photoconductive body is returned into the development unit, agitated, charged and conveyed to the development zone again.
A development unit, disclosed in Japanese Unexamined Patent Application Publication No. 2002-148937, includes a development supply roller 120, as a developer carrying member, for supplying a toner to a development sleeve 110 as a developer carrying member, and a developer limiting roller 130 as a thin layer forming member (as shown in FIG. 2). In this arrangement, the developer is allowed to pass through between the development sleeve 110 and the limiting roller 130 to form the toner on the development sleeve 110 into a thin layer.
However, the toner in the development unit is subject to a large mechanical stress when the toner is formed into a thin layer by the thin layer forming member such as a thin layer forming blade or the developer limiting roller. Typically, an external additive is attached to the periphery of a matrix resin of toner to impart flowability to the toner. Under the presence of mechanical stress, the external additive is buried into the matrix resin. This reduces the flowability of the toner, thereby causing the toner to aggregate. The aggregated toner reduces the amount charge thereof, thereby leading to scumming, and toner supply failure. The toner tends to age rapidly, and maintaining image quality becomes difficult.